The invention relates to gas turbine engines. More particularly, the invention relates to control of blade/shroud interference.
During the operation of a gas turbine engine, there may be various combinations of thermally- and dynamically-induced dimensional changes. One area of particular concern is changes influencing the clearance between compressor blade tips and the adjacent surface of a shroud surrounding the blades. Uncontrolled interference may be catastrophic. Providing sufficient baseline clearance to avoid interference under all anticipated circumstances, however, leaves too large a clearance under other circumstances. The large clearance may result in inefficient operation. The use of rub strips and abradable blade tips may be but a half measure, sacrificially avoiding catastrophic damage upon interference.
A number of systems have been proposed for dynamically accommodating differential expansion. U.S. Pat. No. 4,683,716 identifies a particular segmented shroud compressed radially inward by high pressure air during cruise conditions and expanded by exposure to relatively low pressure air during transients. U.S. Pat. No. 4,844,688 discloses another particular configuration in which high pressure compressed air may be controllably introduced to a chamber to radially position shroud segments. U.S. Pat. No. 5,211,534 discloses another particular configuration in which pressure is applied and released to a pressure tube to radially shift shroud segments. Nevertheless, there remains room for improvement in the art.